A plastic net with a partial to a multiplicity of sprirals between the interstices or crossings of the net filaments is disclosed in my prior U.S. Pat. No. 4,353,956. To make that net, conventional relatively rotating or reciprocating extrusion die members were used with the modification that each orifice of both die members were fed with two different plastic materials characterized by having different properties of contraction and orientation. One material may be a synthetic elastomeric rubber-like material, such as a thermoplastic rubber, and the other a plastic material, such as polyproplene or polyethylene. The net was extruded from the die head in the usual manner, and then the filaments were oriented, as by stretching, well below the melt temperature of the materials, and then releasing. This causes the filaments to contract into helices. The number of helical revolutions or spirals between interstices or crossings may vary from a multiplicity of revolutions to only a partial revolution, this being controlled by the choice of spacing between interstices and the choice and proportions of materials exhibiting the desired properties.
This procedure for manufacturing the net produces satisfactory results for small net structures but becomes increasingly difficult to control as the size of the nets are increased. What is needed is a manufacturing process for my helical net-like structures which is capable of producing the nets to any size with uniform control.